1. Field of the Invention
This invention relates to a drive control system for controlling a automatic guided vehicle on a prearranged path established by a guide means.
2. Description of Related Art
Some types of automatic guided vehicles are equipped with optical sensors for detecting path instruction means by which a prearranged travel path is established on, for example, a floor of a factory. Such a automatic guided vehicle is equipped with a steering control system which selectively use optimum steering gains according to travel speeds in order the automatic guided vehicle to adapt steering characteristics different between forward travel and backward travel. Such a automatic guided vehicle is known from, for example, Japanese Patent Publication No. 62-78613.
While this prior art automatic guided vehicle is advantageous in that selection of steering gains makes over-steering and under-steering as small as possible, it is hard to change steering control characteristics after the loop gain has once been established.
Japanese Unexamined Patent Publication No. 6-259134 describes an autonomous travel vehicle equipped with drive control systems which include a bearing sensor for detecting an absolute location and bearing angle of the vehicle, a direction encoder and a speed encoder. The automonous travel control system performs an operation to estimate an angular speed based on output values from these encoders and makes a comparison of the estimated angular speed with an absolute angular speed. The absolute angular speed is employed to control the vehicle when the difference between these angular speeds is within specified limits, and the estimated angular speed is employed to control the vehicle when the difference between these angular speeds is beyond the specified limits.
In the prior art autonomous travel control changes the speed of vehicle stepwise, a stepwise change of the speed of autonomous travel vehicle causes lateral or right and left sway motion of the vehicle due to a relatively long time spent until electric circuits of the autonomous travel control system becomes stable in operation.